Surface acoustic wave device

ABSTRACT

A surface acoustic wave device includes a piezoelectric substrate, an IDT electrode, support layers, and a cover layer. A distance from a first end of a first partition-support layer to one of the outer-periphery-frame support layers closest to the first end is smaller than a distance from a second end of the first partition-support layer to one of the outer-periphery-frame support layers closest to the second end, and a distance from a first end of a second partition-support layer to one of the outer-periphery-frame support layers closest to the first end is larger than a distance from a second end of the second partition-support layer to one of the outer-periphery-frame support layers closest to the second end.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of priority to Japanese PatentApplication No. 2015-252619 filed on Dec. 24, 2015. The entire contentsof this application are hereby incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to surface acoustic wave devices, and moreparticularly, to a surface acoustic wave device having a wafer levelpackage (WLP) structure.

2. Description of the Related Art

Surface acoustic wave devices are used as band pass filters in wirelesssections, such as radio-frequency (RF) stages and intermediate-frequency(IF) stages, of mobile communication terminals. In recent years,wireless sections in personal digital assistants (PDAs), such ascellular phones and smartphones, have been modularized, and accordingly,there has been a need for a reduction in the size and height of surfaceacoustic wave devices. Thus, packaging technologies for surface acousticwave devices have been improved, and a WLP technology has been proposedin which a chip of a surface acoustic wave device is directly used as apackage. In a surface acoustic wave device, interdigital transducer(IDT) electrodes are provided on a piezoelectric substrate, and thesurface acoustic wave device is packaged so that a hollow space isprovided above the IDT electrodes. In a WLP-type surface acoustic wavedevice, a piezoelectric substrate is directly used as a package thatincludes a hollow space.

In modularization of wireless sections in PDAs, such as cellular phonesand smartphones, there is a need to modularize such wireless sections bysealing them with a resin in order to protect them against externalstress and moisture. When an entire module is sealed with a resin (e.g.,transfer molding), high pressure is applied to individual componentsthat are sealed with the resin, and accordingly, there is a need for amethod for allowing a surface acoustic wave device having a hollow spaceinside thereof to be capable of withstanding such high pressure and tobe capable of withstanding a mold resin that tries to enter the surfaceacoustic wave device (i.e., a method for allowing the surface acousticwave device to have mold resistance or pressure resistance and to have alamination property or a sealing property).

In the related art, as a technology that ensures the mold resistance andthe lamination property of a surface acoustic wave device, a technologyfor providing a partition-support layer (inner support layer), whichfunctions as a spacer, in a hollow space has been proposed (see, forexample, Japanese Patent No. 5141852). In Japanese Patent No. 5141852,the mold resistance of a surface acoustic wave device is ensured bydisposing a partition-support layer, which is made of a resin, at acenter portion of a hollow space so as to be vertically arranged betweena piezoelectric substrate and a cover layer that define the hollowspace.

Here, in order to further improve the mold resistance, providing apartition-support layer, which extends in the lateral and longitudinaldirections when the piezoelectric substrate is viewed in plan, in thehollow space may be considered. FIG. 7 is a layout view of a hollowspace of a surface acoustic wave device according to a reference example(a diagram when a piezoelectric substrate is viewed in plan). FIG. 7illustrates a piezoelectric substrate 11, on which IDT electrodes (notillustrated) have been provided, outer-periphery-frame support layers 20a to 20 d which cover the periphery of the piezoelectric substrate 11,partition-support layers 22 a to 22 c, which are disposed so as topartition the hollow space, and columnar electrodes 17 a to 17 h. Eachof the partition-support layers 22 a to 22 c is vertically arranged onthe piezoelectric substrate 11 in a region in which the IDT electrodesare not disposed, and the partition-support layers 22 a to 22 c support,together with the outer-periphery-frame support layers 20 a to 20 d, acover layer (not illustrated) that defines a ceiling of the hollowspace. When the piezoelectric substrate 11 is viewed in plan, thepartition-support layer 22 c has a substantially crank shape extendingso as to partition the hollow space in the longitudinal and lateraldirections. As a result, reinforcement strength with respect to thecover layer may be enhanced, and the mold resistance of the surfaceacoustic wave device may be improved, whereas if all thepartition-support layers 22 a to 22 c extend in only one direction, thereinforcement strength with respect to the cover layer would not beenhanced, and the mold resistance of the surface acoustic wave devicewould not be improved.

However, in the case where the partition-support layer 22 c having asubstantially crank shape, such as that illustrated in FIG. 7 isprovided, when the cover layer, which is made of a resin, is attached tothe outer-periphery-frame support layers 20 a to 20 d and thepartition-support layers 22 a to 22 c from above, wrinkles are generatedin a portion of the cover layer that is brought into contact with acrank portion of the partition-support layer 22 c, and thepartition-support layer 22 c is embedded into the cover layer. As aresult, the portion of the cover layer in contact with the crank portionof the partition-support layer 22 c, is crushed. For example, whenattaching a cover layer, which has been rolled, to the partition-supportlayer 22 a, the partition-support layer 22 b, and the partition-supportlayer 22 c in this order while stretching the cover layer, when thecover layer is attached to the partition-support layer 22 c, wrinklesare generated in the cover layer, and the cover layer is crushed. As aresult, problems occur in that a portion having a reduced thickness islocally provided in the cover layer, or breakage occurs locally in thecover layer, so that the mold resistance and the lamination property ofthe surface acoustic wave device will not be ensured, and thereliability of the surface acoustic wave device will not be ensured as aresult of the wrinkles, which have been generated in the cover layer,being in contact with the IDT electrodes or wiring electrodes.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention provide a surfaceacoustic wave device having a wafer level package (WLP) structure whosemold resistance, lamination property, and reliability are improved andensured.

A surface acoustic wave device according to a preferred embodiment ofthe present invention includes a piezoelectric substrate, aninterdigital transducer (IDT) electrode that is disposed on a mainsurface of the piezoelectric substrate and that excites a surfaceacoustic wave, support layers each of which is vertically arranged in aregion of the main surface other than a region in which the IDTelectrode is disposed and each of which has a height greater than aheight of the IDT electrode, and a cover layer that is disposed on thesupport layers and that covers the IDT electrode with a hollow spaceinterposed between the cover layer and the IDT electrode. The supportlayers include a plurality of outer-periphery-frame support layers thatare vertically arranged on the main surface around a periphery of theregion in which the IDT electrode is disposed and a plurality ofpartition-support layers each of which is vertically arranged in aregion of the main surface, the region being surrounded by theouter-periphery-frame support layers, the plurality of partition-supportlayers extending so as to be straight or substantially straight in afirst direction, which is parallel or substantially parallel to the mainsurface, and being arranged in a second direction, which is parallel orsubstantially parallel to the main surface and perpendicular to thefirst direction, when the piezoelectric substrate is viewed in plan. Theplurality of partition-support layers include a first partition-supportlayer and a second partition-support layer that are adjacent to eachother in the arrangement of the plurality of partition-support layersand that have a characteristic described below. While the piezoelectricsubstrate is viewed in plan, when an end of the first partition-supportlayer and an end of the second partition-support layer that are orientedin the first direction are referred to as first ends, and another end ofthe first partition-support layer and another end of the secondpartition-support layer that are oriented in a direction opposite to thefirst direction are referred to as second ends, a distance from thefirst end of the first partition-support layer to one of theouter-periphery-frame support layers that is closest to the first end ofthe first partition-support layer is smaller than a distance from thesecond end of the first partition-support layer to one of theouter-periphery-frame support layers that is closest to the second endof the first partition-support layer, and a distance from the first endof the second partition-support layer to one of theouter-periphery-frame support layers that is closest to the first end ofthe second partition-support layer is larger than a distance from thesecond end of the second partition-support layer to one of theouter-periphery-frame support layers that is closest to the second endof the second partition-support layer.

With this configuration, when the piezoelectric substrate is viewed inplan, the partition-support layers have a structure (firstpartition-support layer and second partition-support layer) that isobtained by removing only a longitudinal portion (portion extending inthe second direction) of the crank portion from the partition-supportlayer according to the above-described reference example, which has acrank shape or a substantially crank shape. As a result, the pluralityof partition-support layers extend in the same direction (firstdirection) while maintaining mold resistance the same or substantiallythe same as the mold resistance of the partition-support layer having asubstantially crank shape. Thus, the probability of an occurrence of aproblem in that, when the cover layer, which is made of a resin or othersuitable material, is attached to the outer-periphery-frame supportlayers and the partition-support layers from above, wrinkles aregenerated in the cover layer, and one of the partition-support layers isembedded into the cover layer is reduced. This results in a reduction inthe probability of a portion having a small thickness being providedlocally in the cover layer, and the cover layer is attached to theouter-periphery-frame support layers and the partition-support layersfrom above while maintaining the uniform thickness of the cover layer,so that the mold resistance, the lamination property, and thereliability are ensured. In addition, since the longitudinal portion(portion extending in the second direction) of the crank portion isremoved from the partition-support layer according to the referenceexample, which has a crank shape or a substantially crank shape, theregion of the piezoelectric substrate 11 in which the IDT electrode isto be disposed (electrode-design area) is increased by an amount equalor substantially equal to the longitudinal portion.

In addition, when the piezoelectric substrate is viewed in plan, each ofthe first partition-support layer and the second partition-support layerdoes not need to have a long length so as to divide the hollow spaceinto two spaces and may have a small length, and thus, the probabilityof the region of the piezoelectric substrate in which the IDT electrodeis disposed becoming narrow is reduced.

When viewed from the second direction, a portion of the firstpartition-support layer and a portion of the second partition-supportlayer may preferably be superposed with each other. For example, thelength of a region in which the portion of the first partition-supportlayer and the portion of the second partition-support layer may besuperposed with each other in the first direction may preferably beabout 30 μm or smaller, for example.

Accordingly, since the first partition-support layer and the secondpartition-support layer include the portions which are superposed witheach other when viewed from the second direction, the mold resistance isfurther improved as compared to a case where the first partition-supportlayer and the second partition-support layer are not superposed witheach other.

In addition, when viewed from the second direction, the firstpartition-support layer and the second partition-support layer maypreferably be separated from each other by a predetermined distance inthe first direction. For example, the predetermined distance maypreferably be about 30 μm or smaller, for example.

Accordingly, since the first partition-support layer and the secondpartition-support layer are separated from each other by thepredetermined distance when viewed from the second direction, a largerregion of the piezoelectric substrate in which the IDT electrode isdisposed is ensured as compared to a case where the firstpartition-support layer and the second partition-support layer are notseparated from each other.

In various preferred embodiments of the present invention, a WLP-typesurface acoustic wave device, whose mold resistance, laminationproperty, and reliability are further improved, is provided.

The above and other elements, features, steps, characteristics andadvantages of the present invention will become more apparent from thefollowing detailed description of the preferred embodiments withreference to the attached drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating a surface acoustic wave deviceaccording to a preferred embodiment of the present invention.

FIG. 2A is a cross-sectional view of the surface acoustic wave deviceobtained by cutting the surface acoustic wave device in a planeincluding line IIA-IIA of FIG. 1.

FIG. 2B is a cross-sectional view of the surface acoustic wave deviceobtained by cutting the surface acoustic wave device in a planeincluding line IIB-IIB of FIG. 1.

FIG. 3 is a layout view of a hollow space of the surface acoustic wavedevice illustrated in FIG. 1.

FIGS. 4A to 4F are diagrams illustrating a process of manufacturing thesurface acoustic wave device according to a preferred embodiment of thepresent invention.

FIGS. 5A to 5C are diagrams illustrating examples of the positionalrelationship between a first partition-support layer and a secondpartition-support layer that are included in the surface acoustic wavedevice according to a preferred embodiment of the present invention.

FIG. 6 is a cross-sectional view of a surface acoustic wave deviceaccording to a modification of a preferred embodiment of the presentinvention.

FIG. 7 is a layout view of a hollow space of a surface acoustic wavedevice according to a reference example.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described indetail below with reference to the drawings. Note that the preferredembodiments, which will be described below, are preferred specificexamples of the present invention. Numerical values, shapes, materials,components, arrangement positions and connection configurations of thecomponents, steps, the order of the steps, and other features that aredescribed in the following preferred embodiments are examples and arenot intended to limit the scope of the present invention.

FIG. 1 is a diagram illustrating a surface acoustic wave device 10according to a preferred embodiment of the present invention. As viewedin FIG. 1, the right direction will be referred to as a first direction(positive X-axis direction), and a direction towards the front side andthat is perpendicular to the first direction will be referred to as asecond direction (positive Y-axis direction).

The surface acoustic wave device 10 has a wafer level package (WLP)structure and is preferably, for example, a transmission filter, areception filter, a duplexer, or other suitable surface acoustic wavedevice. The surface acoustic wave device 10 includes a hollow space 19inside thereof, and the hollow space 19 is surrounded by a piezoelectricsubstrate 11, an outer-periphery-frame support layer 20 that is disposedso as to be vertically arranged at an outer peripheral portion of thepiezoelectric substrate 11, and a cover layer 16 that is disposed on theouter-periphery-frame support layer 20. When the piezoelectric substrate11 is viewed in plan, the overall shape of the surface acoustic wavedevice 10 is preferably rectangular or substantially rectangular definedby the X-axis direction and the Y-axis direction. Solder bumps 18 a to18 h are exposed upward at the cover layer 16. The surface acoustic wavedevice 10 is typically soldered to amounting substrate (not illustrated)while being turned upside down from the state illustrated in FIG. 1 withthe solder bumps 18 a to 18 h interposed therebetween.

FIG. 2A is a cross-sectional view of the surface acoustic wave device 10obtained by cutting the surface acoustic wave device in a planeincluding line IIA-IIA of FIG. 1. FIG. 2B is a cross-sectional view ofthe surface acoustic wave device 10 obtained by cutting the surfaceacoustic wave device in a plane including line IIB-IIB of FIG. 1.

The surface acoustic wave device 10 includes the piezoelectric substrate11, IDT electrodes 12, wiring patterns 12 a, terminal electrodes 13,wiring electrodes 14, a protective film 15, the cover layer 16, columnarelectrodes 17, solder bumps 18, the outer-periphery-frame support layer20, and partition-support layers 21.

Preferably, the piezoelectric substrate 11 is a piezoelectric body thatdefines a substrate of the surface acoustic wave device 10 and is madeof, for example, a piezoelectric single crystal, such as lithiumtantalate (LiTaO₃), lithium niobate (LiNbO₃), or quartz crystal, or apiezoelectric ceramic.

Each of the IDT electrodes 12 is a pair of comb-shaped or substantiallycomb-shaped electrodes that is disposed on a main surface (top surface)of the piezoelectric substrate 11 and that excites a surface acousticwave. For example, each of the IDT electrodes 12 is preferably made of ametal, such as Ti, Al, Cu, Au, Pt, Ag, Pd, or Ni, or an alloy, or isdefined by a multilayer body including at least one of theabove-mentioned metals or an alloy.

The wiring patterns 12 a are conductive patterns that connect theplurality of IDT electrodes 12 and connect the IDT electrodes 12 and theterminal electrodes 13 to one another, and the wiring patterns 12 a arepreferably made of, for example, a material similar to that of the IDTelectrodes 12.

The terminal electrodes 13 are electrodes that are connected to the IDTelectrodes 12 and are each disposed at an outer peripheral portion ofthe main surface of the piezoelectric substrate 11, and the terminalelectrodes 13 are preferably made of, for example, a material similar tothat of the IDT electrodes 12.

The wiring electrodes 14 are electrodes that are disposed on theterminal electrodes 13 and that define portions of a wiring pathconnecting the IDT electrodes 12 and the outside of the surface acousticwave device 10 to each other, and the wiring electrodes 14 arepreferably made of, for example, a material similar to that of the IDTelectrodes 12.

The protective film 15 is a layer that covers the IDT electrodes 12 inorder to protect the IDT electrodes 12 and is preferably made of, forexample, a dielectric material, such as silicon oxide or siliconnitride.

The outer-periphery-frame support layer 20 is vertically arranged in aregion of the main surface of the piezoelectric substrate 11 other thana region in which the IDT electrodes 12 have been disposed. Theouter-periphery-frame support layer 20 is one of support layers, each ofwhich has a height larger than the height of each of the IDT electrodes12, and is vertically arranged around the periphery of the region inwhich the IDT electrodes 12 have been disposed. Theouter-periphery-frame support layer 20 is preferably made of, forexample, a material including at least one of a polyimide, an epoxyresin, benzocyclobutene (BCB), polybenzoxazole (PBC)), a metal, andsilicon oxide. Note that, although the outer-periphery-frame supportlayer 20 is vertically arranged on the protective film 15 in the presentpreferred embodiment, the outer-periphery-frame support layer 20 may bevertically arranged directly on the piezoelectric substrate 11 or may bevertically arranged on the wiring patterns 12 a that is provided on thepiezoelectric substrate 11.

Each of the partition-support layers 21 is vertically arranged in aregion of the main surface of the piezoelectric substrate 11 other thanthe region in which the IDT electrodes 12 are disposed. Each of thepartition-support layers 21 is one of the support layers, each of whichhas a height larger than the height of each of the IDT electrodes 12,and is vertically arranged in a region surrounded by theouter-periphery-frame support layer 20. Each of the partition-supportlayers 21 is preferably made of, for example, a material similar to thatof the outer-periphery-frame support layer 20. Note that, although thepartition-support layers 21 are vertically arranged on the protectivefilm 15, which covers the wiring patterns 12 a, in the present preferredembodiment, the partition-support layers 21 may be vertically arrangeddirectly on the wiring patterns 12 a without the protective film 15interposed therebetween or may be vertically arranged directly on thepiezoelectric substrate 11.

The cover layer 16 is a layer that is disposed on the support layers(outer-periphery-frame support layer 20 and partition-support layers 21)and that covers the IDT electrodes 12 with the hollow space 19interposed therebetween and preferably has a multilayer structureincluding a lower layer that is made of for example, a materialincluding at least one of an epoxy resin, urethane, phenol, a polyester,BCB, and PBO and an upper layer that is made of for example, a materialincluding at least one of a polyimide, an epoxy resin, BCB, PBO,silicon, a silicon oxide, LiTaO₃, and LiNbO₃.

The columnar electrodes 17 are electrodes that define portions of awiring path connecting the wiring electrodes 14 and the outside to eachother and that extend through the outer-periphery-frame support layer 20and the cover layer 16, and the columnar electrodes 17 are preferablymade of, for example, a material similar to that of the IDT electrodes12.

The solder bumps 18 are connecting electrodes each having a protrudingshape that are used to solder the surface acoustic wave device 10 to themounting substrate (not illustrated), and the solder bumps 18 arepreferably made of, for example, a material similar to that of the IDTelectrodes 12 or solder.

FIG. 3 is a layout view of the hollow space 19 of the surface acousticwave device 10 illustrated in FIG. 1. Here, in order to simplify FIG. 3,the IDT electrodes 12 and other elements are not illustrated, and FIG. 3illustrates only the piezoelectric substrate on which the IDT electrodes12 are provided, the outer-periphery-frame support layers 20 a to 20 dcovering the periphery of the piezoelectric substrate 11, thepartition-support layers 21 a to 21 g that partition the hollow space19, and the columnar electrodes 17 a to 17 h.

The outer-periphery-frame support layers 20 a to 20 d are components ofthe outer-periphery-frame support layer 20 illustrated in FIG. 1 anddefine a rectangular or substantially rectangular shape surrounding theregion of the main surface of the piezoelectric substrate 11 in whichthe IDT electrodes 12 are disposed. Note that regions 11 a to 11 c ofthe main surface of the piezoelectric substrate 11, each of which issurrounded by one of three dashed line frames in FIG. 3, respectivelycorrespond to a reception filter, an intermediate region positionedbetween the reception filter and a transmission filter, and thetransmission filter where the surface acoustic wave device 10 is aduplexer, for example.

The partition-support layers 21 a to 21 g are specific examplescorresponding to the partition-support layers 21 illustrated in FIG. 2Band are vertically arranged in the region of the main surface of thepiezoelectric substrate 11 surrounded by the outer-periphery-framesupport layer 20. The partition-support layers 21 a to 21 g are aplurality of partition-support layers, and when the piezoelectricsubstrate 11 is viewed in plan, the plurality of partition-supportlayers extend so as to be straight or substantially straight in thefirst direction (positive X-axis direction), which is parallel orsubstantially parallel to the main surface of the piezoelectricsubstrate 11, and are arranged in the second direction (positive Y-axisdirection), which is parallel or substantially parallel to the mainsurface of the piezoelectric substrate 11 and which is perpendicular tothe first direction (positive X-axis direction). In other words, thepartition-support layers 21 a to 21 g extend so as to be straight orsubstantially straight in the first direction (positive X-axisdirection). That is to say, only partition-support layers that areparallel or substantially parallel to one another are provided as thepartition-support layers 21 a to 21 g.

However, preferably, the partition-support layers 21 a to 21 g are notarranged at an equal pitch in the Y-axis direction and do not have thesame width in the Y-axis direction. For example, among the gaps betweenadjacent ones of the partition-support layers 21 a to 21 g, the gapbetween the partition-support layer 21 c and the partition-support layer21 d is the largest, and the gap between the first partition-supportlayer 21 f and the second partition-support layer 21 g is the smallest.Regarding the widths of the partition-support layers 21 a to 21 g, forexample, the widths of the partition-support layer 21 a and thepartition-support layer 21 d are preferably equal or substantially equalto each other and are the largest, and the widths of thepartition-support layer 21 b, the partition-support layer 21 c, thefirst partition-support layer 21 f, and the second partition-supportlayer 21 g are preferably equal or substantially equal to one anotherand are the smallest. The widths of the partition-support layers 21 a to21 g are set while being limited by the size and the position of aregion in which the IDT electrodes 12 are not disposed and, for example,to distribute reinforcement strength, which corresponds to the moldresistance, in the hollow space 19 as uniformly as possible.

In the present preferred embodiment, the partition-support layers 21 ato 21 g preferably do not extend to (are not in contact with) theouter-periphery-frame support layers 20 a to 20 d in order to make theinternal pressure of the hollow space 19 uniform or substantiallyuniform by maintaining the hollow space 19 as a single space.

Here, a characteristic configuration of the present preferred embodimentis that the plurality of partition-support layers 21 a to 21 g includethe first partition-support layer 21 f and the second partition-supportlayer 21 g that are adjacent to each other in the arrangement of theplurality of partition-support layers 21 a to 21 g and that havecharacteristics described below.

While the piezoelectric substrate 11 is viewed in plan, when an end ofthe first partition-support layer 21 f and an end of the secondpartition-support layer 21 g on the first direction (positive X-axisdirection) side are respectively referred to as first ends 21 fr and 21gr, and an end of the first partition-support layer 21 f and an end ofthe second partition-support layer 21 g on a direction (negative X-axisdirection) side, the direction being opposite to the first direction,are respectively referred to as second ends 21 f 1 and 21 g 1, thefollowing two relationships are satisfied.

(1) The distance from the first end 21 fr of the first partition-supportlayer 21 f to the outer-periphery-frame support layer 20 d, which isclosest to the first end 21 fr, is smaller than the distance from thesecond end 21 f 1 of the first partition-support layer 21 f to theouter-periphery-frame support layer 20 b, which is closest to the secondend 21 f 1.

(2) The distance from the first end 21 gr of the secondpartition-support layer 21 g to the outer-periphery-frame support layer20 d, which is closest to the first end 21 gr, is larger than thedistance from the second end 21 g 1 of the second partition-supportlayer 21 g to the outer-periphery-frame support layer 20 b, which isclosest to the second end 21 g 1.

The above two relationships indicate that the first partition-supportlayer 21 f and the second partition-support layer 21 g have a structurethat is obtained by removing only a longitudinal portion (portionextending in the Y-axis direction) of the crank portion from thepartition-support layer 22 c according to the above-described referenceexample, which has a crank shape or a substantially crank shape, (thefirst partition-support layer 21 f and the second partition-supportlayer 21 g are arranged so as to be offset with respect to each other).As a result, the plurality of partition-support layers 21 a to 21 gextend in the same or substantially the same direction (first direction)while maintaining mold resistance at the same or substantially the samemold resistance of the partition-support layer 22 c having a crank shapeor a substantially crank shape. Therefore, the probability of occurrenceof a problem in that, when the cover layer 16, which is made of a resinor other suitable material, is attached to the outer-periphery-framesupport layers 20 a to 20 d and the partition-support layers 21 a to 21g from above, wrinkles are generated in the cover layer 16, and one ofthe partition-support layers is embedded into the cover layer 16 isreduced. This results in a reduction in the probability of a portionhaving a small thickness being provided locally in the cover layer 16,and the cover layer 16 is attached to the outer-periphery-frame supportlayers 20 a to 20 d and the partition-support layers 21 a to 21 g fromabove while maintaining the uniform thickness of the cover layer 16, sothat the mold resistance, the lamination property, and the reliabilityare ensured. In addition, since the longitudinal portion (portionextending in the second direction) of the crank portion is removed fromthe partition-support layer 22 c according to the reference example,which has a crank shape or a substantially crank shape, the region ofthe piezoelectric substrate 11 in which the IDT electrodes 12 are to bedisposed (electrode-design area) is increased by an amount equal orsubstantially equal to the longitudinal portion.

In addition, when the piezoelectric substrate 11 is viewed in plan, eachof the first partition-support layer 21 f and the secondpartition-support layer 21 g does not need to have a long length so asto divide the hollow space 19 into two spaces and may have a smalllength (preferably a length half or approximately half of the length ofthe hollow space 19 in the X-axis direction in the present preferredembodiment), and thus, the probability of the region of thepiezoelectric substrate 11 in which the IDT electrodes 12 are disposedbecoming narrow is reduced.

FIGS. 4A to 4F are diagrams illustrating a non-limiting example of aprocess of manufacturing the surface acoustic wave device 10 accordingto a preferred embodiment of the present invention.

First, as illustrated in FIG. 4A, after the IDT electrodes 12, thewiring patterns 12 a, and the terminal electrodes 13 have been formed onthe main surface of the piezoelectric substrate 11 by a vacuumdeposition method or other suitable method using a photolithographytechnique, for example, the wiring electrodes 14 are formed on theterminal electrodes 13 by a method similar to the above-describedmethod. Then, the protective film 15, which covers the main surface ofthe piezoelectric substrate 11, the IDT electrodes 12, and the wiringpatterns 12 a, is formed by sputtering or other suitable method using aphotolithography technique.

Next, as illustrated in FIG. 4B, the support layers(outer-periphery-frame support layer 20 and partition-support layers 21)are formed into films using a photolithography technique so as to bevertically arranged in a region of the main surface of the piezoelectricsubstrate 11 other than the region in which the IDT electrodes 12 aredisposed. In this case, the film deposition process for the supportlayers continues until the height of each of the support layers islarger than the height of each of the IDT electrodes 12.

Next, as illustrated in FIG. 4C, the cover layer 16, which has beenrolled, is attached to the support layers (outer-periphery-frame supportlayer 20 and partition-support layers 21) from above and is fixed ontothe support layers by being pressed against the support layers. Forexample, in the structure illustrated in FIG. 3, the cover layer 16 ispreferably attached to and fixed onto the outer-periphery-frame supportlayer 20 a, the partition-support layer 21 a, the partition-supportlayer 21 b, the partition-support layer 21 c, the partition-supportlayer 21 d, the first partition-support layer 21 f, the secondpartition-support layer 21 g, the partition-support layer 21 e, and theouter-periphery-frame support layer 20 c so as to be in contact withthese layers by being pressed against the layers in the seconddirection. Here, when the cover layer 16 is attached to the firstpartition-support layer 21 f and the second partition-support layer 21g, since the first partition-support layer 21 f and the secondpartition-support layer 21 g have a structure obtained by removing onlythe longitudinal portion (portion extending in the Y-axis direction) ofthe crank portion from the partition-support layer 22 c according to thereference example, which has a crank shape or a substantially crankshape, (the first partition-support layer 21 f and the secondpartition-support layer 21 g are arranged so as to be offset withrespect to each other), the probability of the occurrence of a problemin that wrinkles are generated in the cover layer 16 and that one of thepartition-support layers is embedded into the cover layer 16 issignificantly reduced.

Next, as illustrated in FIG. 4D, through holes 17 i are formed byremoving portions of the cover layer 16 and portions of theouter-periphery-frame support layer 20 by, for example, radiating alaser beam onto the cover layer 16 and the outer-periphery-frame supportlayer 20, and the wiring electrodes 14 are exposed.

Next, as illustrated in FIG. 4E, the columnar electrodes 17 with whichthe through holes 17 i are filled are formed by, for example, performingelectrolytic plating.

Finally, as illustrated in FIG. 4F, the solder bumps 18 are bonded tothe columnar electrodes 17 by, for example, being pressed against thecolumnar electrodes 17.

Note that, the above-described process is performed on a base materialof the piezoelectric substrate 11 in order to manufacture a plurality ofsurface acoustic wave devices 10 at the same time, and at the end of theprocess, the surface acoustic wave devices 10 are isolated from oneanother by, for example, cutting with a dicing machine the surfaceacoustic wave devices 10 into individual devices.

The WLP-type surface acoustic wave device 10 according to the presentpreferred embodiment preferably is manufactured through a process, suchas the non-limiting example of a manufacturing method described above.

The surface acoustic wave device 10 according to the present preferredembodiment manufactured in the manner described above has the followingcharacteristics. The surface acoustic wave device 10 includes thepiezoelectric substrate 11, the IDT electrodes 12, each of which isdisposed on the main surface of the piezoelectric substrate 11 and eachof which excites a surface acoustic wave, the support layers(outer-periphery-frame support layer 20 and partition-support layers21), each of which is vertically arranged in a region of the mainsurface of the piezoelectric substrate 11 other than the region in whichthe IDT electrodes 12 are disposed, and each of which has a heightlarger than the height of each of the IDT electrodes 12, and the coverlayer 16, which is disposed on the support layers and which covers theIDT electrodes 12 with the hollow space 19 interposed therebetween. Thesupport layers include the outer-periphery-frame support layers 20 a to20 d, which are vertically arranged around the periphery of the regionof the main surface of the piezoelectric substrate 11 in which the IDTelectrodes 12 are disposed, and the plurality of partition-supportlayers 21 a to 21 g that are vertically arranged in the region of themain surface of the piezoelectric substrate 11, the region beingsurrounded by the outer-periphery-frame support layers 20 a to 20 d, theplurality of partition-support layers 21 a to 21 g extending, when thepiezoelectric substrate 11 is viewed in plan, so as to be straight orsubstantially straight in the first direction (positive X-axisdirection), which is parallel or substantially parallel to the mainsurface of the piezoelectric substrate 11, and being arranged in thesecond direction (positive Y-axis direction), which is parallel orsubstantially parallel to the main surface of the piezoelectricsubstrate 11 and which is perpendicular or substantially perpendicularto the first direction (positive X-axis direction). The plurality ofpartition-support layers 21 a to 21 g include the firstpartition-support layer 21 f and the second partition-support layer 21g, which are adjacent to each other in the arrangement of the pluralityof partition-support layers 21 a to 21 g and which have thecharacteristics described below. While the piezoelectric substrate 11 isviewed in plan, when the end of the first partition-support layer 21 fand the end of the second partition-support layer 21 g oriented in thefirst direction (positive X-axis direction) are respectively referred toas the first ends 21 fr and 21 gr, and the end of the firstpartition-support layer 21 f and the end of the second partition-supportlayer 21 g oriented in the direction opposite to the first direction(positive X-axis direction) are respectively referred to as the secondends 21 f 1 and 21 g 1, (1) the distance from the first end 21 fr of thefirst partition-support layer 21 f to the outer-periphery-frame supportlayer 20 d, which is closest to the first end 21 fr, is smaller than thedistance from the second end 21 f 1 of the first partition-support layer21 f to the outer-periphery-frame support layer 20 b, which is closestto the second end 21 f 1, and (2) the distance from the first end 21 grof the second partition-support layer 21 g to the outer-periphery-framesupport layer 20 d, which is closest to the first end 21 gr, is largerthan the distance from the second end 21 g 1 of the secondpartition-support layer 21 g to the outer-periphery-frame support layer20 b, which is closest to the second end 21 g 1.

Accordingly, the first partition-support layer 21 f and the secondpartition-support layer 21 g have a structure, which is obtained byremoving only the longitudinal portion (portion extending in the Y-axisdirection) of the crank portion from the partition-support layer 22 caccording to the reference example, which has a crank shape or asubstantially crank shape, (the first partition-support layer 21 f andthe second partition-support layer 21 g are offset with respect to eachother), and thus, the plurality of partition-support layers 21 a to 21 gextend in the same direction (first direction) while maintaining a moldresistance the same or substantially the same as the mold resistance ofthe partition-support layer 22 c having a crank shape or a substantiallycrank shape. Therefore, the probability of the occurrence of the problemin that, when the cover layer 16, which is made of a resin or othersuitable material, is attached to the outer-periphery-frame supportlayers 20 a to 20 d and the partition-support layers 21 a to 21 g fromabove, wrinkles are generated in the cover layer 16, and that one of thepartition-support layers is embedded into the cover layer 16 is reduced.This results in a reduction in the probability of a portion having asmall thickness being provided locally in the cover layer 16. Inaddition, the cover layer 16 is attached to the outer-periphery-framesupport layers 20 a to 20 d and the partition-support layers 21 a to 21g from above while maintaining the uniform thickness of the cover layer16, and the mold resistance, the lamination property, and thereliability are ensured during a sealing operation using a resin, suchas transfer molding. Furthermore, since the longitudinal portion(portion extending in the second direction) of the crank portion isremoved from the partition-support layer 22 c according to the referenceexample, which has a crank shape or a substantially crank shape, theregion of the piezoelectric substrate 11 in which the IDT electrodes 12are disposed (electrode-design area) is increased by an amount equal orsubstantially equal to the longitudinal portion.

When the piezoelectric substrate 11 is viewed in plan, each of the firstpartition-support layer 21 f and the second partition-support layer 21 gdoes not need to have a long length so as to divide the hollow space 19into two spaces and may have a small length (preferably a lengthapproximately half of the length of the hollow space 19 in the X-axisdirection in the present preferred embodiment), and thus, theprobability of the region of the piezoelectric substrate 11 in which theIDT electrodes 12 are disposed becoming narrow is reduced.

Note that, in the layout illustrated in FIG. 3, although the second end21 f 1 of the first partition-support layer 21 f and the first end 21 grof the second partition-support layer 21 g extend to the same orsubstantially the same position in the X-axis direction when viewed fromthe second direction (positive Y-axis direction), the positionalrelationship between the first partition-support layer 21 f and thesecond partition-support layer 21 g in the first direction (positiveX-axis direction) is not limited to this relationship.

FIGS. 5A-5C is a diagram illustrating examples of the positionalrelationship between the first partition-support layer 21 f and thesecond partition-support layer 21 g, which are included in the surfaceacoustic wave device 10 according to a present preferred embodiment.

In FIG. 5A, when viewed from the second direction (positive Y-axisdirection), a portion of the first partition-support layer 21 f and aportion of the second partition-support layer 21 g are preferablysuperposed with each other in the X-axis direction. Accordingly, sincethe first partition-support layer 21 f and the second partition-supportlayer 21 g include the portions which are superposed with each other inthe X-axis direction when viewed from the second direction (positiveY-axis direction), the mold resistance is further improved as comparedto a case where the first partition-support layer 21 f and the secondpartition-support layer 21 g do not include portions that are superposedwith each other.

Note that it is preferable that the length (superposed width) of aregion in which the portion of the first partition-support layer 21 fand the portion of the second partition-support layer 21 g aresuperposed with each other in the first direction (positive X-axisdirection) be about 30 μm or smaller, for example. This is because, ifthe region in which the portion of the first partition-support layer 21f and the portion of the second partition-support layer 21 g aresuperposed with each other is too large, the region of the piezoelectricsubstrate 11 in which the IDT electrodes 12 are disposed would bereduced.

In FIG. 5B, when viewed from the second direction (positive Y-axisdirection), preferably, the first partition-support layer 21 f and thesecond partition-support layer 21 g extend such that the second end 21 f1 of the first partition-support layer 21 f and the first end 21 gr ofthe second partition-support layer 21 g are located at the same orsubstantially the same position in the X-axis direction. This layout isthe same as that illustrated in FIG. 3.

In FIG. 5C, when viewed from the second direction (positive Y-axisdirection), preferably, the first partition-support layer 21 f and thesecond partition-support layer 21 g are separated from each other by apredetermined distance in the X-axis direction. Accordingly, since thefirst partition-support layer 21 f and the second partition-supportlayer 21 g are separated from each other by the predetermined distancein the X-axis direction when viewed from the second direction (positiveY-axis direction), a larger region of the piezoelectric substrate 11 inwhich the IDT electrodes 12 are disposed is ensured compared with thecase where the first partition-support layer 21 f and the secondpartition-support layer 21 g are not separated from each other.

Note that it is preferable that the predetermined distance be about 30μm or smaller, for example. This is because, if the predetermineddistance is too large, the mold resistance would not be ensured.

Note that the surface acoustic wave device according to the presentinvention is not limited to the structure described in the preferredembodiment described above and may include the columnar electrodes 17that are exposed. FIG. 6 is a cross-sectional view of a surface acousticwave device 10 a according to a modification of a preferred embodimentof the present invention. In the surface acoustic wave device 10 a, thecolumnar electrodes 17 are exposed, and solder bumps are not provided onthe columnar electrodes 17. Advantageous effects similar to those of theabove-described preferred embodiment are able to be obtained byproviding a first partition-support layer 21 f and a secondpartition-support layer 21 g, which are similar to those of theabove-described preferred embodiment, in the surface acoustic wavedevice 10 a. In the surface acoustic wave device 10 a, since theouter-periphery-frame support layer 20 and the cover layer 16 are notdisposed on exposed portions of the columnar electrodes 17, a reductionin the size of the surface acoustic wave device 10 a is able to beachieved. In addition, since solder bumps are not provided on thecolumnar electrodes 17, a further reduction in the height of the surfaceacoustic wave device 10 a is able to be achieved. Furthermore, whenmounting the surface acoustic wave device 10 a, the surface acousticwave device 10 a is able to be connected to a mounting substrate notonly via top surfaces of the columnar electrodes 17 but also via sidesurfaces of the columnar electrodes 17, and thus, the mounting strengthof the surface acoustic wave device 10 a is able to be improved.

Although surface acoustic wave devices according to the presentinvention have been described with reference to preferred embodimentsand modifications thereof, the present invention is not limited thereto.Other preferred embodiments obtained by making various modificationsdevised by those skilled in the art to the preferred embodiments and themodifications or obtained by combining some of the components in thepreferred embodiments and the modifications are also included in thescope of the present invention.

For example, in the above-described preferred embodiments, although onlyone pair of the first partition-support layer 21 f and the secondpartition-support layer 21 g, which have the above-describedcharacteristics (1) and (2), preferably are provided in the surfaceacoustic wave device 10 as illustrated in FIG. 3, two or more pairs ofthe first partition-support layer 21 f and the second partition-supportlayer 21 g may be provided.

In the above-described preferred embodiments, although the firstpartition-support layer 21 f and the second partition-support layer 21 gare preferably arranged in this order in the second direction (positiveY-axis direction), these layers may be arranged in reverse order (in theorder of the second partition-support layer 21 g and the firstpartition-support layer 21 f).

In the above-described preferred embodiments, although the firstpartition-support layer 21 f and the second partition-support layer 21 gpreferably are positioned in the region 11 c, in which the transmissionfilter is provided, the positions of the layers are not limited to thesepositions, and the first partition-support layer 21 f and the secondpartition-support layer 21 g may be positioned in the region 11 a, inwhich the reception filter is provided, or in the region 11 b, whichcorresponds to the intermediate region.

In the above-described preferred embodiments, although the firstpartition-support layer 21 f and the second partition-support layer 21 gpreferably extend from a position near the outer-periphery-frame supportlayer 20 to the center or substantially the center of the hollow space19 in the X-axis direction, the first partition-support layer 21 f andthe second partition-support layer 21 g are not limited to thisarrangement. Each of the first partition-support layer 21 f and thesecond partition-support layer 21 g may extend to a position that iscloser to the outer-periphery-frame support layer 20 than to the centerof the hollow space 19 in the X-axis direction (e.g., a position that isspaced apart from the outer-periphery-frame support layer 20 by anamount equal to approximately one fourth of the size of the hollow space19 in the X-axis direction).

In the above-described preferred embodiments, although thepartition-support layers 21 a to 21 g preferably are arranged so as notto extend to (so as not to be in contact with) the outer-periphery-framesupport layers 20 a to 20 d, the present invention is not limited tothis configuration. A first end and/or a second end of at least one ofthe partition-support layers 21 a to 21 g may extend to (may be incontact with) the outer-periphery-frame support layers 20 a to 20 d.

In the above-described preferred embodiments, although FIG. 3illustrates the layout of the partition-support layers 21 a to 21 g inthe case where the surface acoustic wave device 10 is a duplexer, thesurface acoustic wave device 10 is not limited to a duplexer and may beany type of filter as long as the filter is a WLP-type SAW device.

Preferred embodiments of the present invention can be applied toWLP-type surface acoustic wave devices, and more particularly, to asurface acoustic wave device whose mold resistance, lamination property,and reliability are favorable (e.g., a surface acoustic wave device thatis included in a wireless module in a PDA).

While preferred embodiments of the present invention have been describedabove, it is to be understood that variations and modifications will beapparent to those skilled in the art without departing from the scopeand spirit of the present invention. The scope of the present invention,therefore, is to be determined solely by the following claims.

What is claimed is:
 1. A surface acoustic wave device comprising: apiezoelectric substrate; an interdigital transducer electrode that isdisposed on a main surface of the piezoelectric substrate and thatexcites a surface acoustic wave; support layers each of which isvertically arranged in a region of the main surface of the piezoelectricsubstrate other than a region in which the interdigital transducerelectrode is disposed, and each of the support layers has a heightlarger than a height of the interdigital transducer electrode; and acover layer that is disposed on the support layers and that covers theinterdigital transducer electrode with a hollow space interposed betweenthe cover layer and the interdigital transducer electrode; wherein thesupport layers include: a plurality of outer-periphery-frame supportlayers that are vertically arranged on the main surface of thepiezoelectric substrate around a periphery of the region in which theinterdigital transducer electrode is disposed; and a plurality ofpartition-support layers each of which is vertically arranged in aregion of the main surface, the region being surrounded by theouter-periphery-frame support layers, the plurality of partition-supportlayers extending, when the piezoelectric substrate is viewed in plan,straight or substantially straight in a first direction, which isparallel or substantially parallel to the main surface, and beingarranged in a second direction parallel or substantially parallel to themain surface and perpendicular or substantially perpendicular to thefirst direction; and the plurality of partition-support layers include afirst partition-support layer and a second partition-support layer thatare adjacent to each other in an arrangement of the plurality ofpartition-support layers and that have a characteristic described below:when the piezoelectric substrate is viewed in plan, where an end of thefirst partition-support layer and an end of the second partition-supportlayer that are oriented in the first direction are referred to as firstends, and another end of the first partition-support layer and anotherend of the second partition-support layer that are oriented in adirection opposite to the first direction are referred to as secondends, a distance from the first end of the first partition-support layerto one of the outer-periphery-frame support layers that is closest tothe first end of the first partition-support layer is smaller than adistance from the second end of the first partition-support layer to oneof the outer-periphery-frame support layers that is closest to thesecond end of the first partition-support layer, and a distance from thefirst end of the second partition-support layer to one of theouter-periphery-frame support layers that is closest to the first end ofthe second partition-support layer is larger than a distance from thesecond end of the second partition-support layer to one of theouter-periphery-frame support layers that is closest to the second endof the second partition-support layer.
 2. The surface acoustic wavedevice according to claim 1, wherein a portion of the firstpartition-support layer and a portion of the second partition-supportlayer are superposed with each other when viewed from the seconddirection.
 3. The surface acoustic wave device according to claim 2,wherein a region in which the portion of the first partition-supportlayer and the portion of the second partition-support layer aresuperposed with each other has a length of about 30 μm or smaller in thefirst direction.
 4. The surface acoustic wave device according to claim1, wherein the first partition-support layer and the secondpartition-support layer are separated from each other by a predetermineddistance in the first direction when viewed from the second direction.5. The surface acoustic wave device according to claim 4, wherein thepredetermined distance is about 30 μm or smaller.
 6. The surfaceacoustic wave device according to claim 1, further comprising solderbumps exposed at an outer surface of the cover layer.
 7. The surfaceacoustic wave device according to claim 1, wherein the interdigitalelectrode defines a transmission filter.
 8. The surface acoustic wavedevice according to claim 1, wherein the interdigital electrode definesa reception filter.
 9. The surface acoustic wave device according toclaim 1, wherein the interdigital electrode defines a duplexer.
 10. Thesurface acoustic wave device according to claim 1, wherein thepiezoelectric substrate is made of a piezoelectric single crystal. 11.The surface acoustic wave device according to claim 10, wherein thepiezoelectric single crystal is one of lithium tantalate, lithiumniobate, and quartz crystal.
 12. The surface acoustic wave deviceaccording to claim 1, wherein the interdigital electrode is made of Ti,Al, Cu, Au, Pt, Ag, Pd, or Ni, or an alloy thereof.
 13. The surfaceacoustic wave device according to claim 1, wherein the interdigitalelectrode is covered by a protective film made of a dielectric material.14. The surface acoustic wave device according to claim 1, wherein thesupport layers are made of a material including at least one of apolyimide, an epoxy resin, benzocyclobutene, polybenzoxazole, a metal,and silicon oxide.
 15. The surface acoustic wave device according toclaim 1, wherein the plurality of partition-support layers do not extendto any of the outer-periphery-frame support layers.
 16. The surfaceacoustic wave device according to claim 1, wherein the cover layer has amultilayer structure including a lower layer that is made of a materialincluding at least one of an epoxy resin, urethane, phenol, a polyester,benzocyclobutene, and polybenzoxazole and an upper layer that is made ofa material including at least one of a polyimide, an epoxy resin,benzocyclobutene, polybenzoxazole, silicon, a silicon oxide, lithiumtantalate, and lithium niobate.
 17. The surface acoustic wave deviceaccording to claim 1, further comprising: a reception filter; atransmission filter; an intermediate region disposed between thereception filter and the transmission filter; wherein the receptionfilter and the transmission filter are defined by the interdigitaltransducer electrode.
 18. The surface acoustic wave device according toclaim 17, wherein the first partition-support layer and the secondpartition-support layer are disposed in the intermediate region.